ul,li{
    margin: 0;padding: 0;list-style: none;
}
.nav{
    width: 640px;
    height: 400px;
    border: 1px solid #ccc;
    margin: 100px auto 0;
}
.nav>ul{
    position: relative;
    width: 100%;
    height: 100%;
}
.nav>ul>li{
    width: 200px;
    height: 120px;
    float: left;
    margin: 10px 0 0 10px;
    border-radius: 10px;
    transition:transform 0.2s;
}
.nav>ul>li>img{
    width: 100%;
    height: 100%;
    border-radius: 10px;
}